508 MR. A. W. WATERS ON 



Arthropoma cecilii Avuiouin. 



Flustra cecilii Aud. ' Zool. Egypte,' p. 66 (239), pi. viii. fig. 3 ; 

 see Miss Jelly's catalogue. 



Arthropoma cecilii Levinsen, Morpli & Syst. Studies on the 

 Cheil. Biy. p. 332 (1909). 



Schizoporella cecilii Thornely, " Mar. Poly of the Indian Ocean," 

 Trans, Linn. Soc, Zool. vol. xv. p. 147 (1910). 



In m}^ Report of the Antarctic Bryozoa from the Voyage du 

 S.Y. Belgica, p. 50, I called attention to this group and now 

 Levinsen has given it a name. As I previously said Phonicosia 

 JuUien may belong here, but Jullien's specimens are not suf- 

 ficiently complete to settle the question. 



Log. Distribution general in the north temperate zone, the 

 tropics, and Australia. Prison Island, Zanzibar Channel, on the 

 shore (513), collected by Crossland. 



Fossil. European and Australian Tertiaries. 



OSTHIMOSIA zanzibariensis, sp. n. (PI. LXXIII.figs. 9, 15.) 



Zoarium incrusting seaweed, small, irregular. Zocecia sub- 

 globose, smooth. Oral aperture with distinct sinus, otherwise 

 nearly circular, a small semicircular avicularium at each side of 

 the aperture, and when there is an ovicell usually a second pair 

 of avicularia. Surface of the zocecia imperforate with longi- 

 tudinal ribs in the older zooecia, vicarious avicularia among the 

 zocecia having expanded spatulate mandibles. Ovicell large, wide, 

 globose, pei'forated all over. 



In having the perforated ovicells this is like Cellepora avicularis 

 Hincks, to which it is closely allied, but the median avicularium 

 is absent. A perforated ovicell occurs in G. avicularis H., 

 C. coroncpus B., C. megasovia MacG., C. conica Busk, G. re- 

 doutii * Aud. In the early stages this form resembles Schizo- 

 j)07-ella hiaperta Mich., but vicarious spatulate avicularia are 

 unknown in S. hiaperta. The operculum is thinner than that 

 of G. conica, and the walls also are thinner, I find that G. conica 

 is the young form of a species determined by Busk as G. simo- 

 nensis t B,, an erect cylindrical species. The oral aperture of both 

 C. conica and G. avicularis is slightly larger than that of this 

 species from Prison Island. 



After removing from Gellepora the genera Holoporella and 

 Lagenipora there is the present group with a triangular sinus, 

 the ovicell perforated and the surface of the zooecium imper- 

 forate except near the border, and the group includes G. avicularis 

 H., G. conica Busk, G. coronopus S. Woods, leaving still another 

 group with imperfoi'ate ovicells, but a small semilunar area or 

 mark near the proximal part, and a marked sinus in the oral 

 aperture, as, for example, G. evexa JulL, G. eatonensis B. 



* This is only a variet}' of C. avicularis H. I have a specimen from a sonnding- 

 liiie in the Red Sea, 



t Waters, Zool. Chall. Exp. vol. xxxi. pt. Ixxix. p. 35 (1889), 



